A major radio flare detected from Cyg X-3 with Metsahovi Radio Observatory at 37 GHz

ATel #12668; Karri Koljonen (FINCA/MRO), Marco Berton (FINCA/MRO), Merja Tornikoski (MRO), Anne Lahteenmaki (MRO)
on 18 Apr 2019; 11:19 UT
Credential Certification: Karri Koljonen (karri.koljonen@nyu.edu)

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We report an enhanced flux density at 37 GHz of the microquasar Cyg X-3 (RA 20 32 25.78, DEC +40 57 27.9). Based on the source outburst history, when the Swift/BAT (15-50 keV) flux descends to 0 cts/s (https://swift.gsfc.nasa.gov/results/transients/CygX-3/), and radio flux close 10 mJy level, we can expect a major outburst to happen in tens of days up to one or two months. After descending to this 'hypersoft' state around MJD 58530 (ATel #12510), Cyg X-3 has now emerged from it after two months. A quick-look analysis gives the highest flux density for today as 3.4+/-0.15 Jy (UTC 8:11-8:46), and subsequent measurements show a possible decrease (or variability) in flux. The previous observation at 37 GHz has been carried out on 2019-04-13 at 10:45 UTC, and led to an upper limit of < 0.6 Jy. The 37 GHz observations were made with the 13.7 m diameter Aalto University Metsahovi Radio Observatory telescope, which is a radome enclosed Cassegrain type antenna in Finland (60 d 13' 04'' N, 24 d 23' 35'' E). We encourage further multiwavelength observations of the source to monitor this flaring state.